2Université de Bourgogne

critical weight—that indicates that a sufficient size has nuclear receptors, EcR and Ultraspiracle (USP) (Riddi-been achieved to support pupariation and maturation ford et al., 2001). Interestingly, approximately half of the (Stern and Emlen, 1999; Nijhout, 2003). In laboratory remaining 16 canonical nuclear receptors encoded by cultures of Drosophila melanogaster, the attainment of the Drosophila genome are transcriptionally regulated critical weight correlates with the so-called “70 hr by ecdysone and/or function during metamorphosis, change ” (70 hr after egg laying, near the second-to- implicating a central role for these factors in transduc-ing the ecdysone signal (King-Jones and Thummel, 2005). These receptors are referred to as orphan*Correspondence